Two pathways or coagulation cascades, known as the intrinsic and extrinsic pathways, lead to the formation of a clot in blood. When a human body is injured, the extrinsic pathway is first triggered to control the body's blood coagulation. In addition to a blood sample, the coagulation reaction needs some additional tissue factors. The inactive factor X is catalyzed into factor Xa. The prothrombin (factor II) can be transformed from the factor Xa to the thrombin (factor IIa) by the effects of factor Va, acidic phospholipids and calcium ions. The thrombin then transforms fibrinogen into fibrin, enhancing the platelet of the endothelial cells gathered at the injury. The thrombin can also enhance the role of factor XIII, linking each fibrous protein molecule to a stable fibrin. Therefore, inspecting the prothrombin time not only allows determining whether the function of external activation factors of the coagulation system are normal, but also allows assessing and monitoring oral anticoagulants treatment, liver function, vitamin K deficiency, coagulation factor deficiency, and disseminated intravascular coagulation (DIC) syndrome.
Conventional inspection methods for measuring the prothrombin time analyze the condensation phenomenon of transforming the serum soluble protein into an insoluble protein during blood coagulation. These inspection methods can be realized by detecting optical characteristics, such as changes in color, reflection, refraction, luminescence and fluorescence. Such inspection methods, however, require a substantial number of blood test samples and high purity reagents and are time-consuming, as disclosed in U.S. Pat. No. 5,418,141, the entirety of which is hereby incorporated by reference. Moreover, these inspection methods require long detection times and a significant amount of supplies, resulting in inconvenience and higher costs.
Other conventional inspection methods for measurement of the prothrombin time use electrochemical inspection methods. For example, U.S. Pat. No. 3,699,437, the entirety of which is hereby incorporated by reference, discloses observing the comparative decline rate of resistance from the initial to the lowest point. The calculated result is served as a basis for determining coagulation time in which the impedance measurement is related to the mechanism of blood coagulation. Further, U.S. Pat. Nos. 6,060,323; 6,338,821; 6,066,504; 7,673,622; and 6,046,051, the entirety of each of which is hereby incorporated by reference, disclose electronic sensor devices and a test card assembly for the measurement of the coagulation time of a blood sample. The test card assembly is designed with a single electrode or a plurality of electrodes according to the measurement demands of the device. The sample is contacted with the electrodes, which measure the change in impedance corresponding to the change of viscosity of the blood sample as it coagulates. This technique, however, may result in test errors due to the hematocrit and the electrolyte concentration differences among blood test samples in individuals. U.S. Pat. No. 7,005,857, the entirety of which is hereby incorporated by reference, discloses a coagulation inspection device with automatic collection of blood samples. The coagulation inspection device determines the coagulation time by measuring capacitance or impedance changes between two electrodes. These technologies may, therefore, improve the simplicity of the detection device, but they cannot achieve the relatively higher precision and accuracy that the above-discussed optical detection methods may achieve.
Accordingly, a new biosensor device is needed and described herein for measuring prothrombin time (PT) and hematocrit (HCT), one capable of operating with short test times, simple procedures for the user and while achieving highly accurate results.